In order to meet a variety of forums and new technologies related to the 4th generation mobile communications, the 3rd Generation Partnership Project (3GPP) which aims to provide technical specifications of the 3rd generation mobile communications system has proceeded with research for the Long Term Evolution/Evolved Packet Core (LTE/ETC) technologies since year-end 2004 as a part of efforts to optimize and enhance performances of the 3GPP technologies. The LTE mainly led by the 3GPP SA WG2 relates to research of network technologies which aims to determine a network structure together with the LTE work of the 3GPP TSG RAN and to support mobility between networks of different versions. Recently, the LTE has been considered one of the essential standardization issues of the 3GPP. Such work is to develop the 3GPP to be a system based on the IP and supporting a variety of radio (wireless) connection technologies, and has progressed with the aim of an optimized packet-based system capable of minimizing a transmission delay with enhanced data transmission capability.
Hereinafter, the technical terms used in the present invention will be explained.                MTC function indicates a function to support communications between MTC devices or communications between an MTC device and an MTC server, by which communication is established without human interference, unlike human-to-human connections. Examples of MTC applications may include communications between an automatic vending machine and a server, between a POS (Point of Service) device and a server, and between a water or electricity meter reader and a server. As used herein, the device involved is referred to as an MTC device. As used herein, MTC is also called the name of Machine to Machine communication or object communication.        TA (tracking area) indicates an area to which E-UTRAN provides a service, and includes one or more E-UTRAN cells.        RA (routing area) indicates an area to which GERAN/UTRAN provides a service, and includes one or more GERAN/UTRAN cell.        TAI (Tracking Area Identity) list indicates a list of TAIs that identify the tracking areas a UE can enter without performing a tracking area updating procedure. The TAIs in a TAI list assigned by an MME to a UE pertain to the same MME area. The TAI list has been defined in 3GPP TS 24.301 v9.1.0, and thus detailed explanations thereof will be omitted.        MME (Mobility Management Entity) area indicates a part of a network served by an MME. The MME area consists of one or several Tracking Areas. All cells served by one eNodeB are included in one MME Area. The MME area has been defined in 3GPP TS 23.002 v9.2.0, and thus detailed explanations thereof will be omitted.        UMTS: It is an abbreviation of Universal Mobile Telecommunication System and denotes the 3rd mobile communication network.        EPS: It is an abbreviation of Evolved Packet System, and denotes a core network supporting a Long Term Evolution (LTE) network. It is a network in the form of an evolved UMTS.        NodeB: It is installed outdoors as a base station of the UMTS network, and the size of the cell coverage corresponds to a macro cell.        eNodeB: It is installed outdoors as a base station of the Evolved Packet Core (EPC) network, and the size of the cell coverage corresponds to a macro cell.        UE/MS: User Equipment. It denotes a terminal device.        IMSI: International Mobile Subscriber Identity. It is a unique identifier that is internationally and uniquely assigned to a user in a mobile communication network.        SIM card: Subscriber Identity Module card. It stores user subscriber information such as IMSI.        UICC: Universal Integrated Circuit Card. It has the same meaning as SIM card.        MTC: Machine Type Communication. It occurs between machines without human interference.        MTC device: A UE that performs a specific object with a communication function over a core network. Examples of which include a vending machine and a meter reading machine.        MTC server: A server on a network that manages an MTC device and sends and receives data to and from the MTC device.        MTC Application: An actual application (remote meter reading, tracking transport of goods, etc.) which uses an MTC device and an MTC server.        MTC Feature: Some features are required according to the functions or attributes of a network for supporting an MTC application, that is, according to the purpose of each application. Examples of which include MTC monitoring (required for remote meter reading prepared for equipment loss), low mobility (rare mobility for vending machines).        RAN: Radio Access Network. It is the generic term for 3GPP radio access such as RNC, NodeB, and eNodeB.        HLR (Home Location Register)/HSS (Home Subscriber Server): It is a database (DB) indicating subscriber information of a 3GPP network.        RANAP: It is an abbreviation of Radio Access Network Application Part. It denotes an interface between RAN and a node (MME/SGSN/MSC) which is in charge of the control of a core network.        Cell “camping on” indicates a state that the UE having completed a cell selection/reselection process selects a cell. The cell camping has been defined in 3GPP TS 36.304 v9.1.0, and thus detailed explanations thereof will be omitted.        ISR (Idle mode Signaling Reduction) indicates a service to enhance efficiency of network resources by reducing signaling for location registration when the UE moves between different access networks such as E-UTRAN and UTRAN/GERAN.        ICS (IMS Centralized Services) stably provides a consistent service to an IMS regardless of an access network to which the UE has attached (i.e., even if the UE has attached not only to IP-CAN but also to a CS domain). The ICS has been defined in 3GPP TS 23.292 v9.4.0, and thus detailed explanations thereof will be omitted.        IMS (IP Multimedia Subsystem) indicates a system for providing a multimedia service based on an IP.        Attach indicates a state that a terminal accesses a network node, which includes an attach occurring in the event of handover in a broader sense.        
Hereinafter, the present invention will be explained in more detail with reference to the aforementioned technical terms.
FIG. 1 is a conceptual diagram illustrating a 3GPP service model for MTC support.
Although GSM/UMTS/EPS with the 3GPP standards for supporting MTC are defined to perform communication over a PS network, the present specification describes a method applicable to a CS network as well.
In the current technical specification, the use of an existing 3GPP bearer is suggested for the definition of the network structure. A method using a short message service (SMS) for data exchange between an MTC device and an MTC server was proposed as one of alternative solutions. The use of SMS was proposed, considering that a small amount of digital data including meter reading information and product information will be an object of an MTC application in view of the characteristics of the MTC application, by which an existing SMS method and an IMS-based SMS method can be supported.
In FIG. 1, MTCsms is a data exchange interface using an existing SMS method, and MTCi is a data exchange interface for a 3GPP bearer service and IMS.
FIG. 2 is a signal flowchart illustrating an E-UTRAN initial attach procedure as a conventional data transmission method. FIG. 2 briefly shows TS 23.401 v9.3.0 (2009-12) clause 5.3.2.1 E-UTRAN initial attach procedure, which is an example applied to EPC. As used herein, the attach procedure is generally used when initially entering an E-UTRAN cell and when attempting a connection to EPC. Also, the attach procedure may be used upon handover from non-3GPP access to E-UTRAN.
Hereinafter, explanations will be made with reference to FIG. 2. An attach request message is transmitted from a UE 10 to an MME 30 via an eNB20 (S2-1 to S2-2). An authentication procedure of the UE 10 is performed through an HHS 70 (S2-3). Location information of the UE 10 is registered in the HSS 70 (S2-4). The MME 30 sends a default bearer creation request to the S-GW 40 (S2-5), and a message for default bearer creation is exchanged between the S-GW 40 and a P-GW 50 (S2-6 and S2-8). If necessary, PCRF interaction for an operator policy is performed between the P-GW 50 and a PCRF 60 (S2-7). A default bearer is formed between the P-GW 50 and the S-GW 40, whereupon S-GW and P-GW exchange TEID for data transfer. At this point, downlink data begins to be transmitted from the P-GW 50 to the S-GW 40 unless it is an attach for handover (i.e., initial attach). The TEID (Tunneling Endpoint ID) is a parameter serving as an address for data transmission. Data transmission is possible only when TEID information is known.
An Attach access message, which contains TEID of the S-GW 40, is transmitted from the MME 30 to the eNB 20 (S2-10). Also, this message initiates a radio resource setup of a RAN zone.
Resources of a wireless zone is set up through RRC connection reconfiguration, and a setup result is transmitted to the eNB 20 (S2-11).
An Attach complete message is sent from the UE 10 to the MME 30 via the eNB 20 (S2-13 to S2-14). At this point, the eNB 20 transmits eNB TEID for downlink data reception as well. From this point, uplink data can be transmitted to the S-GW 40 via the eNB 20.
The MME 30 transmits eNB TEID to the S-GW 40 through a Modify bearer request message (S2-15). If necessary, the bearer between the S-GW 40 and the P-GW 50 is updated (S2-16 to S2-17). Afterwards, downlink data can be transmitted to the UE 10 via the eNB 20.
Later, if there is a need to store APN, PDN GW id, etc. in the HSS 70 for mobility to non-3GPP access, the MME 30 undergoes a registration process of the HSS 70 through a Notify Request message (S2-19).
FIG. 3 is a signal flowchart illustrating a tracking area update procedure (TAU procedure). FIG. 3 briefly shows TS 23.401 v9.3.0 (2009-12) clause 5.3.3.1/5.3.3.2 TAU procedure, which is an example applied to EPC. TAU is usually performed when a UE in an idle mode attempts to register a new location.
Hereinafter, explanations will be made with reference to FIG. 3. However, the S-GW/P-GW 51 is an integrated expression of the network elements of S-GW and P-GW for convenience of explanation, this expression does not limit the components and functions of a network.
A TAU request message is transmitted from the UE 10 to the MME 30 via the eNB 20 (S3-1 to S3-2).
The MME 30 sends a context request message from the corresponding UE 10 to an old MME 31, and receives context information from the corresponding UE 10, such as bearer-related information and subscriber information (S3-3 and S3-4). Then, the MME 30 transmits a context acknowledgment of a context response message to the old MME 31 (S3-6). Meanwhile, the MME 30 performs an authentication and security procedure of the UE 10 through the HHS 70 (S3-5).
Steps 7 through 9: the MME 30 sends a bearer creation request to the S-GW/P-GW 51 through a Create Session Request message. If there is no change in S-GW, the MME 30 sends an Update Bearer request message to S-GW (S3-7). If necessary, Modify bearer request/response message are exchange between S-GW and the P-GW 51 as well (not shown in FIG. 3). In the case of using a dynamic PCC, PCRF interaction for an operator policy is performed between P-GW and PCRF.
The MME 30 sends a location update request to the HSS 70 to register a new location of the corresponding UE 10 (S3-10), and the HSS 70 sends a request to the old MME 31 to delete bearer information of the corresponding UE 10 through cancel location request/response message messages (S3-11). The HSS 70 completes a new location registration process by transmitting an update location ACK to the MME 30 (S3-12). A TAU accept message is transmitted in the form of an NAS message from the MME 30 to the UE 10 via the eNB 20 (S3-13).
FIG. 4 is a signal flowchart illustrating a UE triggered service request procedure. FIG. 4 briefly shows TS 23.401 v9.3.0 (2009-12) clause 5.3.4.1 UE Triggered Service Request procedure, which is an example applied to EPC. As used herein, the UE Triggered Service Request procedure is usually performed when the UE 10 starts a new service by initiation or attempts to transmit uplink data as a paging response.
Hereinafter, explanations will be made with reference to FIG. 4.
A Service request message in the form of an NAS message is transmitted to the MME 30 via the eNB 20 (S4-1 to S4-2). Meanwhile, the MME 30 performs an authentication procedure of the UE 10 through the HHS 70.
The MME 30 initiates a radio resource setup of a RAN zone by sending an Initial Context Setup Request message using an S1-AP protocol to eNB (S4-4). At this point, TEID of the S-GW 40 for uplink data transmission is transmitted to the eNB 20. Then, a radio bearer is created in a wireless zone between the UE 10 and the eNB 20 (S4-5). From this point, the UE 10 is capable of uplink data transmission.
The eNB 20 transmits an initial Context Setup Complete message to the MME 30, and sends eNB TEID as well so as to enable downlink data transmission (S4-6).
The ENB TEID is transmitted to the S-GW 40 through a Modify bearer request, and downlink data bearer information is updated (S4-7 to S4-11). If necessary, the bearer between the S-GW 40 and the P-GW 50 is updated (S4-8 to S4-10). In the case of using a dynamic PCC, PCRF interaction for an operator policy is performed between the P-GW 50 and the PCRF 60 (S4-9).
FIG. 5 is a signal flowchart illustrating a network triggered service request procedure.
Referring to FIG. 5, when downlink data reaches the P-GW 50 from an external network, the downlink data is transmitted to the S-GW 40 (S5-1). The S-GW 40 notifies the MME 30 functioning as a control plane about the arrival of downlink data (i.e., Downlink data notification), and receives ACK from the MME 30 (i.e., Downlink data notification ACK) (S5-2).
The MME 30 sends a paging message to the eNBs 20 in the TAU list registered by the corresponding UE 10 (S5-3). Also, the respective eNBs 20 broadcast the paging message to their cell area (S5-4).
Having received the paging message, the corresponding UE 10 sends a Service request message as a response to the network (S5-5). After completion of the UE triggered Service request procedure, the S-GW 40 can transmit downlink data to the UE 10.